As Dennis Derdoski approached the edge of the Grand Canyon for the first time, he wasn't sure what to expect.

The 63-year-old manufacturing executive from suburban Minneapolis said he's traveled the world and seen some sights but was left agape by the panorama: "The depth, the colors, the space. I've seen a lot of fabulous things, but this takes the prize for natural wonders."

"Wow!" agreed Judy Ulrey, 50, who also visited Grand Canyon National Park for the first time this spring. "You can't appreciate it through pictures."

Ulrey, of Combined Locks, Wis., said she was too frightened to trek even a short way into the chasm but reveled at the rim-top view. "It's really something gorgeous."

That's the allure of one of the world's Seven Natural Wonders and a destination to top any must-see list of national parks in America.

The dimensions are stunning: 277 miles long, one-mile deep and up to 18 miles wide. Because of twists and side canyons, a full-circuit hike along the rim would cover more than 2,600 miles.

Scott Thybony, a freelance author who has guided raft trips and treks through the canyon for four decades, said the spectacle looms unique and overwhelming even after hundreds of visits. "Every time I go, it's different, it's new," he said. "The inhuman scale of it is hard to get a handle on. You need to hike into it, take a mule down the trail, float the river, fly over it."

Each year, more than 4 million people from all over the world accept that invitation. They come to take pictures of multihued cliffs sculpted by water and wind over the eons. But they leave with an indelible life experience that begins with that stomach-flipping sensation on the brink.

"People just drop to their knees and feel like the abyss is sucking them in," said Thybony, who has written several books on the canyon.

For those who linger, especially venturing beneath the overlooks, a whole new sensation unfolds: immersion into a geological time warp that affects each individual differently. Some feel a spiritual envelopment. Some, listening to the breeze swoosh against 2 billion-year-old rock layers, encounter new perspectives on life and mortality.

"What is so great about the canyon is the sense of solitude and space," said Bruce Babbitt, the former Arizona governor who oversaw all of the nation's national parks while serving as Interior secretary. "It has this transforming feeling, and you just step away from daily life."

Babbitt, a geologist, said the canyon remains his favorite park, a place that became so intertwined with his life that he published a literary collection by famed authors and visitors called Grand Canyon: An Anthology.

The place is safe enough that children, the elderly and those in wheelchairs can enjoy the splendor, yet dangerous enough that, each year, careless visitors die from falls, heat stroke and dehydration.

For first-timers, the big question is how to experience such an overwhelming attraction. You can hike along trails atop the rim, backpack into the abyss for a camping experience, join a multiday rafting adventure on the Colorado River, ride a mule to rustic cabins or get a bird's-eye view on a helicopter tour.

The mesmerizing scenery cannot be captured in postcards or conjured in poetry. Yet casual tourists find much more to do than gawk. Each day, rangers offer free interpretive classes and treks.

After completing a helicopter tour over the canyon and sidling up to the brink, Richard Parkinson of Richmond, Va., could barely contain his excitement. "It is just fantastic!" he said. "There couldn't be anything more magnificent. In all my 69 years, I never knew Grand Canyon was so big."

Grand Canyon National Park covers more than 1,900 square miles, an area larger than Rhode Island. The more accessible South Rim is open year-round and attracts 90% of the visitors. The remote North Rim is closed each winter.

A National Park entry fee of $25 per vehicle ($12 for cyclists and pedestrians) is valid seven days in both locations. Tours and overnight accommodations, including Grand Canyon lodges and campgrounds, tend to fill up, so visitors should make reservations months in advance.

Tom Mesereau, a spokesman for Xanterra, the company that operates lodging and other concessions in the park, said the experience is more fulfilling for those who plan ahead. (A starting point can be the National Park Service website at www.nps.gov/grca/planyourvisit/index.htm.)

History: Although the Grand Canyon exposes rock layers that are 2 billion years old, the chasm itself was formed by erosion in the past 6 million years. Ancient peoples began to inhabit the canyon about 12,000 years ago. The place was viewed by early explorers and settlers as an obstacle rather than a natural wonder. It was first designated as a preserve in the 1890s.

When visiting: The more popular South Rim is 80 miles north of Flagstaff, Ariz. The Grand Canyon Visitor Center on the South Rim by Mather Point is at South Entrance Road.

Visitor information: (928) 638-7888.

Of note: Many landmarks in the canyon — Shiva Temple and Vulcan's Throne, for example — were named for ancient deities by early geologist Clarence Dutton, a theology school dropout.